Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Balance held at close of period in number of contracts.

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Fair Value Measurements (Narrative) (Details) shares in Millions, $ in Millions	Jun. 30, 2019 USD ($) security	Dec. 31, 2018 USD ($) security	Jun. 30, 2016 shares	Jun. 30, 2015 shares
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for Sale	$ 37,867.5	$ 36,888.8
Trading account securities	$ 0.8	$ 0.3
Visa Class B
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Shares issued (in shares) \| shares			1.1	1.0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of available for sale securities portfolio \| security	1,509	1,479
Available for Sale	$ 32,800.0	$ 31,700.0
Level 2 \| External Pricing
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of available for sale securities portfolio \| security		1,479
Trading account securities	0.8	$ 0.3
Level 3 \| Fair Value, Measurements, Nonrecurring \| Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	$ 27.3	13.8
Level 3 \| Fair Value, Measurements, Nonrecurring \| OREO
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value		$ 0.2